The Modern Warfare variants of Juggernauts are heavily protected by explosive ordnance disposal armor, requiring excessive amounts of damage to kill. When encountered, they are able to deal out massive injuries with a shotgun or a light machine gun. In contrast, the Black Ops and Advanced Warfare variants appear to be wearing body armor, and as a result, don't have as much health.

While they all speak in Russian, the words "Get Sum!" and "Kick Me!" are scrawled on the front and rear groin sections of the Juggernaut's armor. A decal of a skull can also be seen in the armor that covers their shoulders.

Juggernauts will sprint towards the player upon spawning, firing their machine guns non-stop until they get in an unspecified range of their foe in which they slow to a steady stroll. Because of their armor, these mercenaries do not bother to take cover; their only concern is to get as close as possible to their targets. The heavy spray of nonstop suppressing fire can make it very hard to deal damage to them allowing them to rush an opponent unapposed. A loud and distinct bass drum sound will play to indicate the spawn of a juggernaut.

Juggernauts require an inordinate amount of firepower to take down, and flinch only when shot by the most powerful weapons. It is best to use high caliber firearms like the Desert Eagle and Barrett .50cal, as well as explosive weapons like the RPG-7 and Thumper. A direct headshot with the explosive weapons will often take these enemies out in one blow. 10 blocks of C4 or an equivalent amount of claymores is sufficient to kill them quickly as well.

On April 13th, 2012, the official Call of Duty: Modern Warfare 3Facebook page confirmed that "Heavy Armor", like the Juggernaut killstreak, was to appear in Call of Duty: Modern Warfare 2 but was scrapped before it was added to the game.

Robert Bowling also stated it was originally to be a level 4 upgrade for the Juggernaut perk in multiplayer, however this was replaced by Pro versions of perks.[1]

The Juggernauts or "Heavies", as the game files refer to them as, appear in the singleplayer missions "Vorkuta" and "Redemption"

The Juggernauts are visually distinct from their Call of Duty: Modern Warfare 2 counterparts, equipped with what appears to be riot armor, leading them to somewhat resemble the Flak Jacket character model from multiplayer.

When first encountered, they are Soviet prison guards, sent in to quell the Vorkuta escape attempt by trying to stop Viktor Reznov and Alex Mason as they try to break into the armory.
In "Redemption" Juggernauts are part of the Soviet detachment on-board the Rusalka, defending it from attacking American forces.

The ones in Vorkuta wield KS-23 shotguns, while the ones in Redemption use RPKs. The latter can also be put into Last Stand, in which this case they will pull out a Full-AutoCZ75.

Compared to Call of Duty: Modern Warfare 2, Juggernauts in this game are noticeably slower, moving at a steady walk instead of running, although they can sprint (albeit slower than a regular soldier) to catch up with the player if the player is on the far side of the map (they will also sprint when their health is low).

As with Call of Duty: Modern Warfare 2, and unlike their Black Ops counterparts, Juggernauts are tough enemies, with the basic variant capable of withstanding at least 70 assault rifle rounds at close range or around 80 to 90 rounds at long range, while the armored counterpart is significantly more durable. Juggernauts also receive a minor health multiplier in later rounds or higher difficulty maps.

Juggernauts appear in three variants: the regular Juggernaut armed with a PKP Pecheneg, the Riot Shield Juggernaut armed with a Riot Shield and said light machine gun, as well as the Armored Juggernaut which begins to appear in later boss waves and possesses heavier armor (visually similar in appearance to the EOD suit seen in the campaign and multiplayer) which allow them to sustain even more damage than a regular Juggernaut. Juggernauts will never drop their PKP Pecheneg when killed, although Riot Shield Juggernauts will drop their Riot Shield. However, the dropped shield will invariably have its durability almost depleted (note that unlike other modes, player-held Survival mode Riot Shields eventually break from damage).

On Easy difficulty, they mostly appear in waves 10 (one Juggernaut), 15 (two Juggernauts), 20 (three Juggernauts), and 26 (two Armored Juggernauts and one Riot Shield Juggernaut). On the opposite end of the spectrum is Insane difficulty, where they first appear in every sixth wave (waves 6, 11 and 16), and from then on, in every third wave (19, 22, 25, 28, etc.); on Insane, they are accompanied by 6 to 12 normal troops, sometimes dogs, and attack helicopters, increasing the complexity and difficulty of handling the Juggernauts.

They enter the map via an Mi-8 helicopter (which can be attacked but is invulnerable for balance purposes). Once the helicopter is in position, a smoke grenade will be thrown and the Juggernaut will rappel down into the smoke. They will destroy any Sentry Turrets if they see them and/ or if attacked by the turret. The most effective weapons to kill a Juggernaut are explosives (C4 can be deployed under the rope they rappel from and used for an easy kill), shotguns (specifically the automatic models) and light machine guns.

Some types of assault rifles are usable against the Juggernaut, but only high damage ones are able to eliminate a Juggernaut with any practical success, examples would be the CM901 and the MK14, because both possess high damage, and the CM901 is capable of eliminating a Juggernaut at close range with one magazine at earlier waves if the player lands most of the shots in the head, or two magazines if hitting the body. The MK14 can be used if the player is fast enough, and more often than not, will eliminate a Juggernaut probably as fast as any other effective weapon for killing Juggernauts. Another effective method is with the M60E4, the player will need to get close to it and move around it staying out of its sights and shooting it and knife it a few times to take it down.

If the player uses a SMG or machine pistol, keeping a distance from the Juggernaut and aiming at the head can be effective.

Flashbangs are also extremely useful because they can incapacitate a Juggernaut for several seconds and can give the player's team a chance to take it out. Predator missiles and airstrikes are also highly effective against these enemies due to their potential to kill multiple Juggernauts at once. Note that the airstrike will deal much more damage than a Predator, and won't require a direct hit on higher levels, although it is more difficult to use without the Juggernauts killing the player or moving out of the airstrike impact zone due to the wait-time before the AC-130 fires upon them. Flashbangs are useful for pinning them in place while waiting for the airstrike shells to arrive. If you run out of flashbangs, run in circles around them stabbing and shooting an auto shotgun at their general head area. Their extremely low maneuverability will allow the player to escape and never get shot whatsoever.

Juggernaut armor crates can be acquired from the Juggernaut reward for Assault Strike Packages and the Juggernaut Recon reward for Support Strike Packages. All survivors in Infected "Striker vs Jugg" begin with a similar outfit by default and lose it once they are neutralized. The bomb carrier in 'Money in the Denk' is also equipped with heavy armor which disappears when the bomb is planted, when the player is killed, when the player leaves the game or when the match is over. For balance purposes, multiplayer Juggernauts have significantly less health than their Special Ops counterparts, unless they have a Riot Shield, and can easily be disposed of with a heavy explosive, or with headshots; alternatively, players facing these behemoths can simply use team tactics by concentrating substantial amounts of gunfire on them until they fall.

A Juggernaut suit for male and females is available on the Xbox Marketplace, a code for which was included in the Hardened edition of Modern Warfare 3. A t-shirt bearing the Juggernaut icon is also available.

Juggernaut armor crates can be acquired from the Juggernaut and the Maniac rewards for Assault Strike Packages, as well as the Juggernaut Recon reward for Support Strike Packages. Additionally, AI controlled Juggernauts and Recon Juggernauts can be dropped from the Loki and Odin pointstreaks, respectively.

The Juggernaut appears in Call of Duty: Heroes as a Unit. It wields a Riot Shield and a Ranger shotgun. They can absorbe a considerable amount of damage before dying while they slowly take out defensive structures such as Sentry Turrets and Howitzer Cannons. Combined with the RD1 healing drone, they can become difficult to defend against an enemy attack.

The Juggernaut helmet emblem can be earned by getting a three killstreak with a riot shield without dying.

The Juggernaut's helmet says R7130.

Juggernauts do not use melee. Even if a player stands next to one, it will keep firing its weapon.

Juggernauts speak in the Special Ops mission, "Armor Piercing", and sometimes speak in the Special Ops mission, "Snatch & Grab", where one can hear some Russian dialogues while all the Shadow Company soldiers speak English.

Juggernauts will generally spawn as close to the player as possible. Unless an allied chopper (not Perk Care Package Chopper, it must be dropping off Delta or Riot Shield personnel) is in the airspace, they will always spawn in the immediate area of the player. This will apply if a player is on one end of the map, and the other player on the other, one Juggernaut will go after whichever one is closest to it.

All Juggernaut models present in multiplayer are of the Armored Juggernaut variant.

A calendar depicting a Juggernaut on a beach entitled "Summer Juggernaut" can be found in various places throughout Call of Duty: Modern Warfare 3. Note the Call of Duty: Modern Warfare 2 model.

Armored Juggernauts also appear to be staturally larger than many of their comrades including other Juggernauts, with their character models standing a head higher than others. This likely was a design decision to make them stand out on the battlefield as well as be bigger and easier targets to hit in order to counter their massive damage intake.